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RE: WANTED: Futterman H3 OTL project - Harvard Electronics or Tech Instruments
Posted by unlisted on June 25, 2022 at 10:30:53:
That's a good point about checking for an uplevel board setup. George Kaye kindly gave me the setup information when he last worked on the amps and they look like standard OTL3 set points, but it's always good to double check. Fortunately, the other amp is working fine so I have a baseline.
I spent quite a lot of time trying to identify the transistors, but other than ubiquitous TO-92 cases I was unable to find any markings even with magnifying glasses and excellent lighting on either amp.
I had George Kaye update the audio circuits with new resistors and caps, given the substantial improvements in component transparency and electrical behavior over the years, along with any other updates required (Dynamicaps, Black Gates, Vishay, Audio Note, etc.). For this reason I think the board and components are in good shape, but I do worry nonetheless. New capacitor power supply banks would certainly get them working optimally now.